U.S. Pat. No. 4,490,421 Levy, and U.S. Pat. No. 5,264,260, Saab, describe PET balloons. U.S. Pat. No. 4,906,244, Pinchuk et al, and U.S. Pat. No. 5,328,468, Kaneko, describe polyamide balloons. U.S. Pat. No. 4,950,239, Gahara, and U.S. Pat. No. 5,500,180, Anderson et al describe balloons made from polyurethane block copolymers. U.S. Pat. No. 5,556,383, Wang et al, and U.S. Pat. No. 6,146,356, Wang et al, describe balloons made from polyether-block-amide copolymers and polyester-block-ether copolymers. U.S. Pat. No. 6,270,522, Simhambhatla, et al, describes balloons made from polyester-block-ether copolymers of high flexural modulus. U.S. Pat. No. 5,344,400, Kaneko, describes balloons made from polyarylene sulfide. U.S. Pat. No. 5,833,657, Reinhart et al, describes balloons having a layer of polyetheretherketone. All of these balloons are produced from extruded tubing of the polymeric material by a blow-forming radial expansion process.
A typical method for forming medical device balloons includes molding the balloon from a hollow parison, for instance an extruded tubular parison. The mold form for such processes is adapted to receive the parison of thermoplastic material and has a cavity into or through which the parison extends. Heat is applied to the mold, for instance by immersion in a heated fluid, to soften the thermoplastic material. Concurrently, or in some sequence of heating and pressurization, the parison is pressurized to radially expand the softened thermoplastic material until it contacts and conforms to the shape of the cavity. This typical method may be practiced in a variety of known ways, for instance with or without an axial stretch step, which may be performed concurrent with or prior to radial expansion and at temperature above or below a glass transition temperature. The parison may be expanded in several steps, each of which may be accompanied by a prior or concurrent axial stretching step. A heat setting step or an annealing step may be performed after the balloon has been molded.
Mold forms for medical device balloons are typically provided with a highly polished or glassy cavity surface which is unbroken, at least over the body surface. In some cases, however a simple heated tube of larger diameter than the parison is used, so that the balloon end cones are free-formed. In a further alternative a balloon may be free-blown in a heated media with cone end forms used to confine the balloon ends.
High strength medical device balloons formed in the manner used for such applications as angioplasty and stent placement in cardiovascular vessels are well known. Typically such balloons are designed to provide a nominal inflated diameter of 6 mm or less. Recently, applications for even larger balloons of similar high strength have been identified.
WO 98/03218 describes techniques for preparing large diameter balloons (5-30 mm dia.), using tubular parisons formed of certain block copolymer materials and incorporating an annealing technique to widen the range of diameters obtainable over the range of useful inflation pressures. The balloons of WO 98/03218 are useful in gastrointestinal surgical procedures.
As balloon size increases, the increasing distance between the walls of the mold and the parison within the mold can cause a higher variability in the balloons obtained, possibly due to increased variability in the location of initiation. The ability to control the initiation location is typically difficult and delicate, as control of initiation requires control of the temperature gradient location within the mold. Conventional fluid-heated immersion molding devices do not allow for repeatable, accurate control of molding initiation location. With larger diameter balloons, this lack of control can negatively affect properties and yields. Balloon properties which may be negatively affected include wall thickness uniformity, position of key transitions associated with cone wall mass removal, and ultimately balloon performance, ability to be delivered, and overall balloon consistency. Therefore a need remains for improvements in balloon blowing processes, particularly for large diameter balloons.